Abstract: The characteristic of the Infrared Search and Track System (IRST) is analyzed, and several typical design methods of IRST that applied broadly at present are compared. For the demand of the ground aerial defense and alertness infrared system design, a new system design method based on line-array-scan imaging and servo circling is proposed. The key part of the realization of the real-time signal process subsystem is explained. The characteristic of the new design method is its capability to realize both searching and tracking in a single system with low cost, it can realize the fast 360° whole airspace searching and target surveillance, and can also precisely track the key target and measure its distance, then come into being the three-dimensional track of the target. The new design provides the system with the genuine function of the optoelectronic radar. The outfield test and the measured data validate the detect capability of the system design.